Edit and Mark
EDMK D1(L1,B1),D2(B2)
Op
Code
LL1
SS1
B1D1 D1D1 B2D2 D2D2
Packed decimal fields can be converted to a character format using the EDMK instruction.
Additionally, editing symbols and features like commas, decimal points, and leading zero
suppression can be included in the character version of the packed decimal field that is being
edited. EDMK is equivalent to the ED instruction but offers additional functionality which will be
covered later in this discussion.
The first step in editing a packed decimal field is to create an “edit word” which is a pattern of
what the character output of the edit process should look like. Typically, the edit word is moved
to a field in the output buffer which is being built, prior to printing. Then the packed decimal field
is “edited” into the output field, destroying the copy of the edit word.
First, we consider how to construct an appropriate edit word for a given packed decimal field.
This can be accomplished by defining a string of hexadecimal bytes that represents the edit word.
Each byte in the edit word corresponds to a byte in the edited character representation. In
creating the edit word there are a collection of standard symbols which are used to describe each
byte:
X’40’
This symbol, which represents a space, is usually coded as the first byte of the
edit word where it acts as a “fill character”. The fill character is used to replace
leading zeroes which are not “significant”.
X’20’
Called a “digit selector”, this byte represents a position in which a
significant digit from the packed field should be placed.
X’21’
This hexadecimal byte represents a digit selector and a significance starter.
Significance starts when the first non-zero digit is selected. Alternatively, we
can force significance to start by coding a single x’21’ in the edit word. In this
case, significance starts in the byte following the x’21’. Significance is
important because every significant digit is printed, even if it is a leading zero.
X’6B’
This is the EBCDIC code for a comma.
X’4B’
This is the EBCDIC code for a decimal point.
X’60’
This is the EBCDIC code for a minus sign. This symbol is sometimes coded on
the end of an edit word when editing signed fields. The x’60’ byte will be
replaced with the fill character if the number being edited is positive. If the
number is in fact negative, the x’60’ will not be “filled”, and the negative sign will
appear in the edited output.
X’C4C2’ The EBCDIC version of “DB” (Debit). This functions like the x’60’. Coding
these symbols at the end of an edit word causes “DB” to appear in the output
if the field being edited is negative, otherewise the “DB” is “filled”.
X’C3D9’ The EBCDIC version of “CR” (Credit). This functions like the Debit symbol
above. When the number being edited is negative, the “CR” symbol will
appear in the edited output, otherwise it will be “filled”.
X’5C’
The EBCDIC symbol for an asterisk. This character is sometimes used as
a fill character when editing dollar amounts on checks.
We now consider a sample edit word and the output it would create for several packed fields.
EDWD
AOUT
APK
DC
DC
DC
X’4020206B2021204B202060’
CL11
PL4’45387’
Assume we execute the instructions below,
MVC
EDMK
AOUT,EDWD
AOUT,APK
First, the edit word is moved to a field in the output buffer. Then the packed field is “edited” into
the output field. The results are illustrated in the diagram below.
APK
00
45
38
7C
EDWD
40
20
20
6B
20
21
20
4B
20
20
60
AOUT
40
40
40
40
F4
F5
F3
4B
F8
F7
40
The diagram indicates the results of the edit process: The fill character (x’40’) is unaffected, and
is left in its position. The first decimal digit, 0, is “selected” by the first x’20’, and since leading 0’s
are not significant, the x’20’ is replaced by the fill character. The second digit, 0, is also selected,
and it too, is filled with a x’40’. Since significance has not started, the x’6B’ is filled with x’40’.
The first non-zero digit, 4, is selected and this signals that significance has started. (Any nonzero digit which is selected turns on the significance indicator.) Each digit after the 4 will appear
in the edited result. The “4” is replaced with its character equivalent - x’F4’. At this point, the
address of AOUT+4 (the position occupied by the first significant digit x’F4’, is copied into register
1. (The ED instruction would not initialize register 1.) Afterward, the “5” is selected and its x’20’
is replaced with x’F5’. The “3” is selected and is represented as x’F3’. The x’4B’, a decimal point,
remains unaffected. The “8” is selected and is represented as x’F8’. The “7” is selected and is
represented as x’F7’. Since the number being edited is positive, the x’60’ is filled with x’40’. The
final result would print as “ 453.87 “.
Consider a second edit which uses the same edit word as in the previous example, but with a
different value for APK.
EDWD
AOUT
DC
DC
X’4020206B2021204B202060’
CL11
APK
DC
PL4’-7’
Again we execute the same sequence of instructions.
MVC
EDMK
AOUT,EDWD
AOUT,APK
APK
00
00
00
7D
EDWD
40
20
20
6B
20
21
20
4B
20
20
60
AOUT
40
40
40
40
40
40
F0
4B
F0
F7
60
As in every edit, the x’40’ fill character is unaffected by the edit process. The first and second
digits, both 0, are selected, and since they are leading 0’s and significance has not started, they
are filled with x’40’. The x’6B’ is also filled with x’40’ since significance has not started. The next
two digits, both 0, are selected and filled. Since the x’21’ selected a leading 0, the significance
indicator is turned on - significance starts with the next digit. This means that all other digits will
appear in a character representation, even if they are leading 0’s. All other editing symbols will
be printed as well. Unlike the previous example, register 1 is not initialized because a significant
digit was never encountered while the significance indicator was off. The fifth digit, 0, is selected
and represented as x’F0’. The x’4B’ is preserved. The next two digits, 0 and 7, are selected and
represented as x’F0’ and x’F7’. Finally, since the APK contains a negative number, the x’60’ is
preserved. The final result would print as “
0.07-”.
It is important to understand that ED and EDMK are equivalent instructions except that under
certain conditions, EDMK will change the contents of register 1. To be precise, EDMK sets
register 1 to the address of the first non-zero digit in the target field if the corresponding
significant digit in the source field was encountered while the significance indicator was off.
Otherwise, register 1 is unaffected. This gives rise to the common practice of initializing register
1 with the address of the byte following the significance starter (x’21’) in the target field prior to
issuing the EDMK instruction. By doing this, the programmer can be assured that register 1 is
pointing at the first significant digit in the target, regardless of the manner in which significance
was started. Consider the example below.
XOUT
EDWD
XPK
MVC
LA
EDMK
...
DS
DC
DS
XOUT,EDWD
R1,XOUT+4
XOUT,XPK
SET UP EDIT WORD
POINT AT SIG.STARTER+1
EDIT THE DATA
CL7
X’402020214B2020’
PL3
Suppose XPK contains x’00000C’. After editing, XOUT contains “ .00”, and register 1 contains
the address of the decimal point. In this case the significance was turned on by the significance
starter.
On the other hand, suppose XPK contains x’05643C’. After editing, XOUT contains “ 56.43”,
and register 1 contains the address of the “5” XOUT. In this case significance was started
because a non-zero digit was selected while significance was off. In both of the previous cases,
register 1 contains the address of the first significant digit. The address in register 1 could be
used to insert an edititing character in front of the first significant digit:
MVI
0(R1),C’$’
FLOAT A DOLLAR SIGN
Examples
Some Unrelated EDMK’s:
APK
AOUT
AEDWD
DC
DS
DC
MVC
LA
ED
BPK
BOUT
BEDWD
DC
DS
DC
MVC
LA
ED
CPK
COUT
CEDWD
DC
DS
DC
MVC
LA
ED
DPK
DOUT
DEDWD
EPK
EOUT
EEDWD
PL2’123’
X‘123C’
CL4
X’40202120’
...
Result:
AOUT,AEDWD
R1,AOUT+3
AOUT,APK
AOUT = X’40F1F2F3’ - ‘ 123’
REGISTER 1 CONTAINS ADDRESS OF AOUT+1
PL2’0’
X‘000C’
CL4
X’40202120’
...
Result:
BOUT,BEDWD
R1,BOUT+3
BOUT,BPK
BOUT = X’404040F0’ - ‘
’
REGISTER 1 CONTAINS ADDRESS OF BOUT+3
PL2’0’
X‘000C’
CL4
X’40212020’
...
Result:
COUT,CEDWD
R1,COUT+2
COUT,CPK
COUT = X’404040F0’ - ‘ 00’
REGISTER 1 CONTAINS ADDRESS OF COUT+3
DC
DS
DC
PL2’0’
X‘000C’
CL4
X’5C202120’
ASTERISK IS USED AS A FILL CHARACTER
MVC
LA
ED
...
DOUT,DEDWD
R1,DOUT+3
DOUT,DPK
DC
DS
DC
MVC
LA
ED
Result:
DOUT = X’5C5C5CF0’ - ‘***0’
REGISTER 1 CONTAINS ADDRESS OF DOUT+3
PL2’-300’
X’300D’ NEGATIVE NUMBER
CL5
X’4020212060’
...
Result:
EOUT,EEDWD
R1,EOUT+3
EOUT,EPK
EOUT = X’4040F3F0’ - ‘ 300-’
REGISTER 1 CONTAINS ADDRESS OF EOUT+1
Tips
1. There are two errors that beginners make when using EDMK :
1) The number of x’20’s and x’21’s does not match the number of decimal digits in the field
being edited. This is a critical error. If the packed field has length “n”, the number of
x’20’s and x’21’s is 2n - 1. For example, if you are editing a packed field of length 6, the
edit word must contain exactly 11 x’20’s and x’21’s. A bad edit word will produce
unpredictable output.
2) The output field size does not match the edit word size. For example, suppose you coded
the following,
AEDWD
DC
X’402020202120’
AOUT
DS
CL5
When the edit word is moved to AOUT, the last byte of the edit word is not moved since
the edit word is 6 bytes and the target field is 5 bytes. The effect is that we are using an
incorrect edit word, even though the definition of the edit word was correct.
2) When editing, start with the packed field and design an edit word that matches it. Then define
the output field to match the edit word. For example, if we start with a packed field of length 3 (5
decimal digits), we could design x’402021204B2020’ as an appropriate edit word (5 x’20’s and
x’21’s). Since the edit word is 7 bytes long, we would design a 7 byte output field to hold the edit
word.
XPK
DS
PL3
XEDWD
DC
X’402021204B2020’
XOUT
DS
CL7
...
MVC
XOUT,XEDWD
LA
R1,XOUT+3
EDMK
XOUT,XPK
3) Be sure to initialize R1 before issuing the EDMK instruction. R1 should contain the address of
the byte following the significance starter (x’21’).